1. Field of the Invention
Aspects of one or more embodiments relate to an electrophotographic image forming apparatus to perform color registration using different patterns in different operation modes and a color registration method thereof.
2. Description of the Related Art
A traditional electrophotographic image forming apparatus (such as a laser printer, a digital copier, etc.) forms an electrostatic latent image on the surface of a photosensitive medium charged with a predetermined potential by scanning light onto the photosensitive medium, develops the electrostatic latent image into a visible image by applying a toner as a developing agent to the electrostatic latent image, and transfers and fixes the developed image onto a piece of paper. An electrophotographic color image forming apparatus creates a color image by supplying four colors of toners (black K, yellow Y, magenta M, and cyan C) to a photosensitive medium and overlapping the resulting different color images with one another.
Two color image creation schemes are generally available for the electrophotographic color image forming apparatus: a single-pass type using four optical scanning units and four photosensitive media, and a multi-pass type using a single optical scanning unit and a single photosensitive medium. When the electrophotographic color image forming apparatus, especially the single-pass electrophotographic color image forming apparatus, fails to accurately overlap the images of different colors at intended positions, image quality is degraded, as is the case with blurs at the edges of a color image. As this occurs due to interaction between a plurality of factors including developer replacement, an increased number of printed papers, etc., color registration may be required to align the images of the respective colors with one another. In this context, the single-pass color image forming apparatus is configured to create high-quality color images through Auto Color Registration (ACR) that triggers color registration automatically, each time various composite factors occur, such as developer replacement, an increase in the number of pieces of printed papers, and the like.
To implement the ACR, the single-pass color image forming apparatus prints ACR patterns of a predetermined length (offset correction patterns for black K, yellow Y, magenta M, and cyan C for use in color registration) on a transfer belt and receives light reflected from each color offset correction pattern through an ACR sensor, thereby recognizing the toner transfer position of each color. With respect to the position of one reference color (e.g. black), the positions of the other colors are adjusted based on the sensed toner transfer positions, such that the images of the respective colors are aligned overlapped at correction positions. However, the ACR patterns of the predetermined length should be printed on a transfer belt for each color registration, taking a large amount of toner. The resulting increased ACR process time does not satisfy user convenience.